34 CLASS III. GASTEROPODA. ORDER III. CERVICOBRANCHIATA. 
did not fail to discover that this property is in no way analogous to the 
common growth of bivalve mollusks. When the animal was at length 
examined by De Blainville, the closest affinity he could establish was that 
it might perhaps indicate a transition to the Brachiopoda, though not pos- 
sibly belonging to the same class. The fact is, that the Hipponyces are 
true cephalous mollusks, belonging to the order of cervicobranchiate Gas- 
teropoda, and intimately allied, as originally conjectured by Defrance and 
Lamarck, to the Pileopses ; the two muscular impressions are very simi- 
lar (compare Fig. 2,3 and4, Plate CXLV. with Fig. 2. Plate CXLVI)) ; 
indeed, Deshayes, as well as other authors of the present day, still refuses 
to separate them. 
Like the basal plate of the Calyptrea lithedaphus (vide Pl. CXLIV. 
Fig. 5, 6 and 7.) the cup of Hipponyx can only be considered as an irre- 
gular accessory appendage deposited by the foot to facilitate the attach- 
ment of the animal, and therefore unnecessary to its existence. But 
the Hipponyces do not always exercise this property ; they are, indeed, 
as often found without the cup as with it ; for when they adhere to other 
shells, the same object is gained by absorbing a suitable place of attach- 
ment, on which may be traced the same muscular impressions. In this 
state they constitute a genus which is distinguished in Gray’s classifica- 
tion by the title of Sabia. 
The shell of Hipponyx may be described as being obliquely conoidal, 
cap-shaped, and sometimes, perhaps generally, supported upon a solid, 
testaceous cup ; the vertex is bent backwards, and both the shell and 
the cup exhibit two strong muscular impressions, which are rounded 
anteriorly, and connated posteriorly in the form of a horse-shoe. 
We have selected two fossil species as the most characteristic exam- 
ples of this genus. Fig. 1 to 6 represent the shell of the first in different 
stages of growth; fig. 7, the outside of the cup; and fig. 8 and 9, the 
inside in different states. Fig. 10 and 13 represent different views of the 
outside of the shell of the second species ; fig. 11, 14 and 15, of the inside 
of the same; and fig. 12 and 16 show the inside of two different speci- 
mens of the cup attached to portions of other shells. 
